Antibodies are drawing attention as pharmaceuticals as they are highly stable in plasma (blood) and have few side effects. Of these, a number of IgG-type antibody pharmaceuticals are available on the market and many antibody pharmaceuticals are currently under development (Non-patent Documents 1 and 2).
Almost all antibody pharmaceuticals currently available on the market are of the IgG1 subclass. IgG1 type antibodies are expected be useful as anti-cancer antibody pharmaceuticals since they can bind to Fcγ receptor and exert ADCC activity. However, when it comes to antibody pharmaceuticals intended for neutralizing biological activity of an antigen, the binding of the Fc domain to Fcγ receptor, which is important for effector functions such as ADCC, can cause unnecessary side effects, and thus it is preferable to eliminate such binding activity (Non-patent Document 3). Furthermore, since Fcγ receptor is expressed on antigen-presenting cells, molecules that bind to Fcγ receptor tend to be presented as antigens. It has been reported that immunogenicity is and can be enhanced by linking a protein or peptide to the Fc domain of IgG1 (Non-patent Document 4 and Patent Document 1). Interaction between the antibody Fc domain and Fcγ receptor is thought to be a cause of the serious side effects encountered in phase-I clinical trials of TGN1412 (Non-patent Document 5). Thus, binding to Fcγ receptor is considered unfavorable in antibody pharmaceuticals intended for neutralizing the biological activity of an antigen from the perspective of side effects and immunogenicity.
A method for impairing the binding to Fcγ receptor is to alter the subtype of the IgG antibody from IgG1 to IgG2 or IgG4; however, this method cannot completely inhibit the binding (Non-patent Document 6). One of the methods reported for completely inhibiting the binding to Fcγ receptor is to artificially alter the Fc domain. For example, the effector functions of anti-CD3 antibodies and anti-CD4 antibodies cause side effects. Thus, amino acids that are not present in the wild type sequence were introduced into the Fcγ-receptor-binding domain of Fc (Non-patent Documents 3 and 7), and clinical trials are currently being conducted to assess anti-CD3 antibodies and anti-CD4 antibodies that have a mutated Fc domain and do not bind to Fcγ receptor (Non-patent Documents 5 and 8). Alternatively, Fcγ receptor-nonbinding antibodies can be prepared by altering the Fcγ R-binding sites of IgG1 (positions 233, 234, 235, 236, 327, 330, and 331 in the EU numbering; hereafter abbreviated as position X (EU numbering)) to an IgG2 or IgG4 sequence (Non-patent Document 9 and Patent Document 2). However, these molecules contain new non-native peptide sequences of nine to twelve amino acids, which may have a potential to become a T-cell epitope peptide and thus pose an immunogenicity risk. There is no previous report on Fcγ receptor-nonbinding antibodies that have overcome these problems.
Meanwhile, physicochemical properties of antibody proteins, in particular, homogeneity and stability, are very crucial in the development of antibody pharmaceuticals. For the IgG2 subtype, heterogeneity caused by disulfide bonds in the hinge region has been reported (Non-patent Documents 10, 16, 17, and 18 and Patent Document 3). It is not easy to manufacture them as a pharmaceutical in a large scale while maintaining differences of desired product/related substance-related heterogeneity between productions. Thus, single substances are desirable as much as possible for antibody molecules developed as pharmaceuticals. In the present invention, differences in heterogeneity among productions can be understood, for example, as differences in heterogeneity among production lots. Heterogeneity in the production lots can be evaluated quantitatively by determining the diversity of molecular weight and structure of the produced antibody molecules.
IgG2 and IgG4 are unstable under acidic conditions. IgG type antibodies are in general exposed to acidic conditions in the purification process using Protein A and the virus inactivation process. Thus, attention is needed regarding the stability of IgG2 and IgG4 during these processes, and it is preferable that antibody molecules developed as pharmaceuticals are also stable under acidic conditions. Natural IgG2 and IgG4, and Fcγ receptor-nonbinding antibodies derived from IgG2 or IgG4 (Non-patent Documents 6 and 7 and Patent Document 2) have such problems. It is desirable to solve these problems when developing antibodies into pharmaceuticals.
IgG1-type antibodies are relatively stable under acidic conditions, and the degree of heterogeneity caused by disulfide bonds in the hinge region is also lower in this type of antibodies. However, IgG1-type antibodies are reported to undergo non-enzymatic peptide bond cleavage in the hinge region in solutions when they are stored as formulations, and as a result, Fab fragments are generated as impurities (Non-patent Document 11). It is desirable to overcome the generation of impurities when developing antibodies into pharmaceuticals.
Furthermore, for heterogeneity of the C-terminal sequence of an antibody, deletion of C-terminal amino acid lysine residue, and amidation of the C-terminal amino group due to deletion of both of the two C-terminal amino acids, glycine and lysine, have been reported (Non-patent Document 12). It is preferable to eliminate such heterogeneity when developing antibodies into pharmaceuticals.
The constant region of an antibody pharmaceutical aimed at neutralizing an antigen preferably has a sequence that overcomes all the problems described above. However, a constant region that meets all the requirements has not been reported.
A preferred form of antibody pharmaceutical administration in chronic autoimmune diseases and such is thought to be subcutaneous formulation. Low-cost, convenient antibody pharmaceuticals that can be administered subcutaneously at longer intervals can be provided by increasing the half-life of an antibody in the plasma to prolong its therapeutic effect and thereby reduce the amount of protein administered, and by conferring the antibody with high stability so that high concentration formulations can be prepared.
In general, subcutaneous formulations need to be high-concentration formulations. From the perspective of stability and such, the concentration limit of IgG-type antibody formulations is generally thought to be about 100 mg/ml (Non-patent Document 13). Thus, it was a challenge to secure stability at high concentrations. However, there has been no report published on the improvement of the stability of IgG at high concentrations by introducing amino acid substitutions into its constant region. A method for prolonging the antibody half-life in plasma has been reported and it substitutes amino acids in the constant region (Non-patent Documents 14 and 15); however, introduction of non-native sequences into the constant region is unpreferable from the perspective of immunogenicity risk.
As described above, when the purpose of an antibody pharmaceutical is to neutralize an antigen, it is preferable that all of the problems described above have been overcome with regard to its constant-region sequence. However, a constant region that meets all the requirements has not been reported. Thus, there is a demand for antibody constant regions that have overcome the problems described above.
Documents of related prior arts for the present invention are described below.